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<a name="Document-classes" class="anchor"></a>
<a name="Document-classes-1" class="anchor"></a>
<h2 class="chapter">Document classes</h2>

<a name="index-document-classes" class="anchor"></a>
<a name="index-classes-of-documents" class="anchor"></a>
<a name="index-_005cdocumentclass" class="anchor"></a>

<p>The document&rsquo;s overall class is defined with this command, which is
normally the first command in a LaTeX source file.
</p>
<div class="example">
<pre class="example">\documentclass[<var>options</var>]{<var>class</var>}
</pre></div>

<a name="index-article-class" class="anchor"></a>
<a name="index-report-class" class="anchor"></a>
<a name="index-book-class" class="anchor"></a>
<a name="index-letter-class" class="anchor"></a>
<a name="index-slides-class" class="anchor"></a>
<p>The following document <var>class</var> names are built into LaTeX.
(Many other document classes are available as separate packages;
see <a href="latex2e_2.html#Overview">Overview</a>.)
</p>
<dl compact="compact">
<dt><code>article</code></dt>
<dd><a name="document-classes-article" class="anchor"></a><p>For a journal article, a presentation, and miscellaneous general use.
</p>
</dd>
<dt><code>book</code></dt>
<dd><a name="document-classes-book" class="anchor"></a><p>Full-length books, including chapters and possibly including front
matter, such as a preface, and back matter, such as an appendix
(see <a href="latex2e_25.html#Front_002fback-matter">Front/back matter</a>).
</p>
</dd>
<dt><code>letter</code></dt>
<dd><a name="document-classes-letter" class="anchor"></a><p>Mail, optionally including mailing labels 
(see <a href="latex2e_26.html#Letters">Letters</a>).
</p>
</dd>
<dt><code>report</code></dt>
<dd><a name="document-classes-report" class="anchor"></a><p>For documents of length between an <code>article</code> and a <code>book</code>,
such as technical reports or theses, which may contain several chapters.
</p>
</dd>
<dt><code>slides</code></dt>
<dd><a name="document-classes-slides" class="anchor"></a><p>For slide presentations&mdash;rarely used today.  In its place the
<code>beamer</code> package is perhaps the most prevalent (see <a href="latex2e_29.html#beamer-template">beamer template</a>).
</p>
</dd>
</dl>

<p>Standard <var>options</var> are described in the next section.
</p>


<hr>
<a name="Document-class-options" class="anchor"></a>
<a name="Document-class-options-1" class="anchor"></a>
<h3 class="section">Document class options</h3>

<a name="index-document-class-options" class="anchor"></a>
<a name="index-options_002c-document-class" class="anchor"></a>
<a name="index-class-options" class="anchor"></a>
<a name="index-global-options" class="anchor"></a>

<p>You can specify <em>global options</em> or <em>class options</em> to the
<code>\documentclass</code> command by enclosing them in square brackets.  To
specify more than one <var>option</var>, separate them with a comma.
</p>
<div class="example">
<pre class="example">\documentclass[<var>option1</var>,<var>option2</var>,...]{<var>class</var>}
</pre></div>

<p>Here is the list of the standard class options.
</p>
<a name="index-10pt-option" class="anchor"></a>
<a name="index-11pt-option" class="anchor"></a>
<a name="index-12pt-option" class="anchor"></a>
<p>All of the standard classes except <code>slides</code> accept the following
options for selecting the typeface size (default is <code>10pt</code>):
</p>
<div class="example">
<pre class="example">10pt  11pt  12pt
</pre></div>

<a name="index-a4paper-option" class="anchor"></a>
<a name="index-a5paper-option" class="anchor"></a>
<a name="index-b5paper-option" class="anchor"></a>
<a name="index-executivepaper-option" class="anchor"></a>
<a name="index-legalpaper-option" class="anchor"></a>
<a name="index-letterpaper-option" class="anchor"></a>
<p>All of the standard classes accept these options for selecting the paper
size (these show height by width):
</p>
<dl compact="compact">
<dt><code>a4paper</code></dt>
<dd><p>210 by 297mm (about 8.25 by 11.75&nbsp;inches)
</p>
</dd>
<dt><code>a5paper</code></dt>
<dd><p>148 by 210mm (about 5.8 by 8.3&nbsp;inches)
</p>
</dd>
<dt><code>b5paper</code></dt>
<dd><p>176 by 250mm (about 6.9 by 9.8&nbsp;inches)
</p> 
</dd>
<dt><code>executivepaper</code></dt>
<dd><p>7.25 by 10.5&nbsp;inches
</p> 
</dd>
<dt><code>legalpaper</code></dt>
<dd><p>8.5 by 14&nbsp;inches
</p> 
</dd>
<dt><code>letterpaper</code></dt>
<dd><p>8.5 by 11&nbsp;inches (the default)
</p></dd>
</dl>

<a name="index-_005cpdfpagewidth" class="anchor"></a>
<a name="index-_005cpdfpageheight" class="anchor"></a>
<a name="index-package_002c-geometry" class="anchor"></a>
<a name="index-geometry-package" class="anchor"></a>

<p>When using one of the engines pdfLaTeX, LuaLaTeX, or XeLaTeX
(see <a href="latex2e_2.html#TeX-engines">TeX engines</a>), options other than <code>letterpaper</code> set
the print area but you must also set the physical paper size.  One way
to do that is to put <code>\pdfpagewidth=\paperwidth</code> and
<code>\pdfpageheight=\paperheight</code> in your document&rsquo;s preamble.
<a name="index-package_002c-geometry-1" class="anchor"></a>
<a name="index-geometry-package-1" class="anchor"></a>
</p>
<p>The <code>geometry</code> package provides flexible ways of setting the print
area and physical page size.
</p>
<a name="index-draft-option" class="anchor"></a>
<a name="index-final-option" class="anchor"></a>
<a name="index-fleqn-option" class="anchor"></a>
<a name="index-landscape-option" class="anchor"></a>
<a name="index-leqno-option" class="anchor"></a>
<a name="index-openbib-option" class="anchor"></a>
<a name="index-titlepage-option" class="anchor"></a>
<a name="index-notitlepage-option" class="anchor"></a>
<p>Miscellaneous other options:
</p>
<dl compact="compact">
<dt><code>draft</code></dt>
<dt><code>final</code></dt>
<dd><a name="index-black-boxes_002c-omitting" class="anchor"></a>
<p>Mark (<code>draft</code>) or do not mark (<code>final</code>) overfull boxes with a
black box in the margin; default is <code>final</code>.
</p>
</dd>
<dt><code>fleqn</code></dt>
<dd><a name="index-flush-left-equations" class="anchor"></a>
<a name="index-centered-equations" class="anchor"></a>
<a name="index-equations_002c-flush-left-vs_002e-centered" class="anchor"></a>
<p>Put displayed formulas flush left; default is centered.
</p>
</dd>
<dt><code>landscape</code></dt>
<dd><a name="index-landscape-orientation" class="anchor"></a>
<a name="index-portrait-orientation" class="anchor"></a>
<p>Selects landscape format; default is portrait.
</p>
</dd>
<dt><code>leqno</code></dt>
<dd><a name="index-left_002dhand-equation-numbers" class="anchor"></a>
<a name="index-right_002dhand-equation-numbers" class="anchor"></a>
<a name="index-equation-numbers_002c-left-vs_002e-right" class="anchor"></a>
<p>Put equation numbers on the left side of equations; default is the right side.
</p>
</dd>
<dt><code>openbib</code></dt>
<dd><a name="index-bibliography-format_002c-open" class="anchor"></a>
<p>Use &ldquo;open&rdquo; bibliography format.
</p>
</dd>
<dt><code>titlepage</code></dt>
<dt><code>notitlepage</code></dt>
<dd><a name="index-title-page_002c-separate-or-run_002din" class="anchor"></a>
<p>Specifies whether there is a separate page for the title information and
for the abstract also, if there is one.  The default for the
<code>report</code> class is <code>titlepage</code>, for the other classes it is
<code>notitlepage</code>.
</p></dd>
</dl>

<p>The following options are not available with the <code>slides</code> class.
</p>
<a name="index-onecolumn-option" class="anchor"></a>
<a name="index-twocolumn-option" class="anchor"></a>
<a name="index-oneside-option" class="anchor"></a>
<a name="index-twoside-option" class="anchor"></a>
<a name="index-openright-option" class="anchor"></a>
<a name="index-openany-option" class="anchor"></a>
<dl compact="compact">
<dt><code>onecolumn</code></dt>
<dt><code>twocolumn</code></dt>
<dd><p>Typeset in one or two columns; default is <code>onecolumn</code>.
</p>
</dd>
<dt><code>oneside</code></dt>
<dt><code>twoside</code></dt>
<dd><a name="index-_005cevensidemargin" class="anchor"></a>
<a name="index-_005coddsidemargin" class="anchor"></a>
<p>Selects one- or two-sided layout; default is <code>oneside</code>, except
that in the <code>book</code> class the default is <code>twoside</code>.
</p>
<p>For one-sided printing, the text is centered on the page.  For two-sided
printing, the <code>\evensidemargin</code> (<code>\oddsidemargin</code>) parameter
determines the distance on even (odd) numbered pages between the left
side of the page and the text&rsquo;s left margin, with <code>\oddsidemargin</code>
being 40% of the difference between <code>\paperwidth</code> and
<code>\textwidth</code>, and <code>\evensidemargin</code> is the remainder.
</p>
</dd>
<dt><code>openright</code></dt>
<dt><code>openany</code></dt>
<dd><p>Determines if a chapter should start on a right-hand page; default is
<code>openright</code> for <code>book</code>, and <code>openany</code> for <code>report</code>.
</p></dd>
</dl>

<a name="index-clock-option-to-slides-class" class="anchor"></a>
<p>The <code>slides</code> class offers the option <code>clock</code> for printing
the time at the bottom of each note.
</p>

<hr>
<a name="Additional-packages" class="anchor"></a>
<a name="Additional-packages-1" class="anchor"></a>
<h3 class="section">Additional packages</h3>

<a name="index-loading-additional-packages" class="anchor"></a>
<a name="index-packages_002c-loading-additional" class="anchor"></a>
<a name="index-additional-packages_002c-loading" class="anchor"></a>
<a name="index-_005cusepackage" class="anchor"></a>
<p>Load a package <var>pkg</var>, with the package options given in the comma-separated
list <var>options</var>, as here.
</p>
<div class="example">
<pre class="example">\usepackage[<var>options</var>]{<var>pkg</var>}.
</pre></div>

<p>To specify more than one package you can separate them with a comma,
as in <code>\usepackage{<var>pkg1</var>,<var>pkg2</var>,...}</code>, or use multiple
<code>\usepackage</code> commands.
</p>
<a name="index-global-options-1" class="anchor"></a>
<a name="index-options_002c-global" class="anchor"></a>
<p>Any options given in the <code>\documentclass</code> command that are unknown
to the selected document class are passed on to the packages loaded with
<code>\usepackage</code>.
</p>

<hr>
<a name="Class-and-package-construction" class="anchor"></a>
<a name="Class-and-package-construction-1" class="anchor"></a>
<h3 class="section">Class and package construction</h3>

<a name="index-document-class-commands" class="anchor"></a>
<a name="index-commands_002c-document-class" class="anchor"></a>
<a name="index-new-class-commands" class="anchor"></a>

<p>You can create new document classes and new packages.  For instance, if
your memos must satisfy some local requirements, such as a
standard header for each page, then you could create a new class
<code>smcmemo.cls</code> and begin your documents with
<code>\documentclass{smcmemo}</code>.
</p>
<p>What separates a package from a document class is that the commands in a
package are useful across classes while those in a document class are
specific to that class.  Thus, a command to set page headers is for a
package while a command to make the page headers say <code>Memo from the
SMC Math Department</code> is for a class.
<a name="index-class-and-package-difference" class="anchor"></a>
<a name="index-difference-between-class-and-package" class="anchor"></a>
</p>
<p>Inside of a class or package file you can use the at-sign <code>@</code> as a
character in command names without having to surround the code
containing that command with <code>\makeatletter</code> and
<code>\makeatother</code>.  See <a href="latex2e_12.html#g_t_005cmakeatletter-_0026-_005cmakeatother">\makeatletter &amp; \makeatother</a>. This allow
you to create commands that users will not accidentally redefine.
Another technique is to preface class- or package-specific commands with
some string to prevent your class or package from interfering with
others. For instance, the class <code>smcmemo</code> might have commands
<code>\smc@tolist</code>, <code>\smc@fromlist</code>, etc.
</p>



<hr>
<a name="Class-and-package-structure" class="anchor"></a>
<a name="Class-and-package-structure-1" class="anchor"></a>
<h4 class="subsection">Class and package structure</h4>

<a name="index-class-and-package-structure" class="anchor"></a>
<a name="index-class-file-layout" class="anchor"></a>
<a name="index-package-file-layout" class="anchor"></a>
<a name="index-options_002c-document-class-1" class="anchor"></a>
<a name="index-options_002c-package" class="anchor"></a>
<a name="index-class-options-1" class="anchor"></a>
<a name="index-package-options" class="anchor"></a>

<p>A class file or package file typically has four parts.  
</p><ol>
<li> In the <em>identification part</em>, the file says that it is a LaTeX
package or class and describes itself, using the <code>\NeedsTeXFormat</code>
and <code>\ProvidesClass</code> or <code>\ProvidesPackage</code> commands.

</li><li> The <em>preliminary declarations part</em> declares some commands and
can also load other files. Usually these commands will be those needed
for the code used in the next part.  For example, an <code>smcmemo</code>
class might be called with an option to read in a file with a list of
people for the to-head, as <code>\documentclass[mathto]{smcmemo}</code>, and
therefore needs to define a command
<code>\newcommand{\setto}[1]{\def\@tolist{#1}}</code> used in that
file.

</li><li> In the <em>handle options part</em> the class or package declares
and processes its options.  Class options allow a user to start their
document as <code>\documentclass[<var>option list</var>]{<var>class
name</var>}</code>, to modify the behavior of the class.  An example is when you
declare <code>\documentclass[11pt]{article}</code> to set the default
document font size.  

</li><li> Finally, in the <em>more declarations part</em> the class or package usually does
most of its work: declaring new variables, commands and fonts, and
loading other files.
</li></ol>

<p>Here is a starting class file, which should be saved as <samp>stub.cls</samp>
where LaTeX can find it, for example in the same directory as the
<samp>.tex</samp> file.
</p>
<div class="example">
<pre class="example">\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{stub}[2017/07/06 stub to start building classes from]
\DeclareOption*{\PassOptionsToClass{\CurrentOption}{article}}
\ProcessOptions\relax
\LoadClass{article}
</pre></div>
<a name="index-class-file-example" class="anchor"></a>

<p>It identifies itself, handles the class options via the default of
passing them all to the <code>article</code> class, and then loads the
<code>article</code> class to provide the basis for this class&rsquo;s code.
</p>
<p>For more, see the official guide for class and package writers, the
Class Guide, at
<a class="external" href="http://www.latex-project.org/help/documentation/clsguide.pdf">http://www.latex-project.org/help/documentation/clsguide.pdf</a> (much
of the descriptions here derive from this document), or the tutorial
<a class="external" href="https://www.tug.org/TUGboat/tb26-3/tb84heff.pdf">https://www.tug.org/TUGboat/tb26-3/tb84heff.pdf</a>.
</p>

<hr>
<a name="Class-and-package-commands" class="anchor"></a>
<a name="Class-and-package-commands-1" class="anchor"></a>
<h4 class="subsection">Class and package commands</h4>
<a name="index-class-and-package-commands" class="anchor"></a>
<a name="index-commands_002c-class-and-package" class="anchor"></a>

<p>These are the commands designed to help writers of classes or packages.
</p>
<dl compact="compact">
<dt><code>\AtBeginDvi{specials}</code></dt>
<dd><a name="index-_005cAtBeginDvi" class="anchor"></a>
<p>Save in a box register things that are written to the <samp>.dvi</samp> file
at the beginning of the shipout of the first page of the document.
</p>
</dd>
<dt><code>\AtEndOfClass{<var>code</var>}</code></dt>
<dt><code>\AtEndOfPackage{<var>code</var>}</code></dt>
<dd><a name="index-_005cAtEndOfClass" class="anchor"></a>
<a name="index-_005cAtEndOfPackage" class="anchor"></a>
<p>Hook to insert <var>code</var> to be executed when LaTeX finishes
processing the current class or package.  You can use these hooks
multiple times; the <code>code</code> will be executed in the order that you
called it.  See also <a href="latex2e_8.html#g_t_005cAtBeginDocument">\AtBeginDocument</a>.
</p>
</dd>
<dt><code>\CheckCommand{<var>cmd</var>}[<var>num</var>][<var>default</var>]{<var>definition</var>}</code></dt>
<dt><code>\CheckCommand*{<var>cmd</var>}[<var>num</var>][<var>default</var>]{<var>definition</var>}</code></dt>
<dd><a name="index-_005cCheckCommand" class="anchor"></a>
<a name="index-_005cCheckCommand_002a" class="anchor"></a>
<a name="index-new-command_002c-check" class="anchor"></a>
<p>Like <code>\newcommand</code> (see <a href="latex2e_12.html#g_t_005cnewcommand-_0026-_005crenewcommand">\newcommand &amp; \renewcommand</a>) but does
not define <var>cmd</var>; instead it checks that the current definition of
<var>cmd</var> is exactly as given by <var>definition</var> and is or is not 
<a name="index-long-command" class="anchor"></a>
<em>long</em> as expected.  A long command is a command that accepts
<code>\par</code> within an argument.  The <var>cmd</var> command is expected to be
long with the unstarred version of <code>\CheckCommand</code>.  Raises an
error when the check fails.  This allows you to check before you start
redefining <code>cmd</code> yourself that no other package has already
redefined this command.
</p>
</dd>
<dt><code>\ClassError{<var>class name</var>}{<var>error text</var>}{<var>help text</var>}</code></dt>
<dt><code>\PackageError{<var>package name</var>}{<var>error text</var>}{<var>help text</var>}</code></dt>
<dt><code>\ClassWarning{<var>class name</var>}{<var>warning text</var>}</code></dt>
<dt><code>\PackageWarning{<var>package name</var>}{<var>warning text</var>}</code></dt>
<dt><code>\ClassWarningNoLine{<var>class name</var>}{<var>warning text</var>}</code></dt>
<dt><code>\PackageWarningNoLine{<var>package name</var>}{<var>warning text</var>}</code></dt>
<dt><code>\ClassInfo{<var>class name</var>}{<var>info text</var>}</code></dt>
<dt><code>\PackageInfo{<var>package name</var>}{<var>info text</var>}</code></dt>
<dt><code>\ClassInfoNoLine{<var>class name</var>}{<var>info text</var>}</code></dt>
<dt><code>\PackageInfoNoLine{<var>package name</var>}{<var>info text</var>}</code></dt>
<dd><a name="index-_005cClassError" class="anchor"></a>
<a name="index-_005cPackageError" class="anchor"></a>
<a name="index-_005cClassWarning" class="anchor"></a>
<a name="index-_005cPackageWarning" class="anchor"></a>
<a name="index-_005cClassWarningNoLine" class="anchor"></a>
<a name="index-_005cPackageWarningNoLine" class="anchor"></a>
<a name="index-_005cClassInfo" class="anchor"></a>
<a name="index-_005cPackageInfo" class="anchor"></a>
<a name="index-_005cClassInfoNoLine" class="anchor"></a>
<a name="index-_005cPackageInfoNoLine" class="anchor"></a>
<p>Produce an error message, or warning or informational messages.
</p>
<p>For <code>\ClassError</code> and <code>\PackageError</code> the message is
<var>error text</var>, followed by TeX&rsquo;s <code>?</code> error prompt. If the
user then asks for help by typing <code>h</code>, they see the <var>help
text</var>.
</p>
<p>The four warning commands are similar except that they write
<var>warning text</var> on the screen with no error prompt.  The four info
commands write <var>info text</var> only in the transcript file.  The
<code>NoLine</code> versions do not show the number of the line generating the
message, while the other versions do show that number.
</p>
<p>To format the messages, including the <var>help text</var>: use
<code>\protect</code> to stop a command from expanding, get a line break with
<code>\MessageBreak</code>, and get a space with <code>\space</code> when a space
character does not allow it, like after a command.  Note that LaTeX
appends a period to the messages.
</p>
</dd>
<dt><code>\CurrentOption</code></dt>
<dd><a name="index-_005cCurrentOption" class="anchor"></a>
<p>Expands to the name of the currently-being-processed option.  Can only
be used within the <var>code</var> argument of either <code>\DeclareOption</code>
or <code>\DeclareOption*</code>.
</p>
</dd>
<dt><code>\DeclareOption{<var>option</var>}{<var>code</var>}</code></dt>
<dt><code>\DeclareOption*{<var>code</var>}</code></dt>
<dd><a name="index-_005cDeclareOption" class="anchor"></a>
<a name="index-_005cDeclareOption_002a" class="anchor"></a>
<a name="index-class-options-2" class="anchor"></a>
<a name="index-package-options-1" class="anchor"></a>
<a name="index-options_002c-class" class="anchor"></a>
<a name="index-options_002c-package-1" class="anchor"></a>
<p>Make an option available to a user to invoke in their
<code>\documentclass</code> command.  For example, the <code>smcmemo</code> class
could have an option <code>\documentclass[logo]{smcmemo}</code> allowing
users to put the institutional logo on the first page.  The class file
must contain <code>\DeclareOption{logo}{<var>code</var>}</code> (and later,
<code>\ProcessOptions</code>).
</p>
<p>If you request an option that has not been declared, by default this
will produce a warning like <code>Unused global option(s): [badoption].</code>
Change this behaviour with the starred version
<code>\DeclareOption*{<var>code</var>}</code>.  For example, many classes extend
an existing class, using a declaration such as
<code>\LoadClass{article}</code>, and for passing extra options to the
underlying class use code such as this.
</p>
<div class="example">
<pre class="example">\DeclareOption*{%
\PassOptionsToClass{\CurrentOption}{article}%
}
</pre></div>

<p>Another example is that the class <code>smcmemo</code> may allow users to keep
lists of memo recipients in external files.  Then the user could invoke
<code>\documentclass[math]{smcmemo}</code> and it will read the file
<code>math.memo</code>.  This code handles the file if it exists and otherwise
passes the option to the <code>article</code> class.
</p>
<div class="example">
<pre class="example">\DeclareOption*{\InputIfFileExists{\CurrentOption.memo}{}{%
    \PassOptionsToClass{\CurrentOption}{article}}}
</pre></div>

</dd>
<dt><code>\DeclareRobustCommand{<var>cmd</var>}[<var>num</var>][<var>default</var>]{<var>definition</var>}</code></dt>
<dt><code>\DeclareRobustCommand*{<var>cmd</var>}[<var>num</var>][<var>default</var>]{<var>definition</var>}</code></dt>
<dd><a name="index-_005cDeclareRobustCommand" class="anchor"></a>
<a name="index-_005cDeclareRobustCommand_002a" class="anchor"></a>
<a name="index-new-command_002c-definition" class="anchor"></a>
<p>Like <code>\newcommand</code> and <code>\newcommand*</code> (see <a href="latex2e_12.html#g_t_005cnewcommand-_0026-_005crenewcommand">\newcommand &amp; \renewcommand</a>) but these declare a robust command, even if some code
within the <var>definition</var> is fragile.  (For a discussion of robust and
fragile commands see <a href="latex2e_12.html#g_t_005cprotect">\protect</a>.) Use this command to define new
robust commands or to redefine existing commands and make them
robust. Unlike <code>\newcommand</code> these do not give an error if macro
<var>cmd</var> already exists; instead, a log message is put into the
transcript file if a command is redefined.
</p>
<p>Commands defined this way are a bit less efficient than those defined
using <code>\newcommand</code> so unless the command&rsquo;s data is fragile and the
command is used within a moving argument, use <code>\newcommand</code>.
</p>
<a name="index-package_002c-etoolbox" class="anchor"></a>
<a name="index-etoolbox-package" class="anchor"></a>
<p>The <samp>etoolbox</samp> package offers the commands
<code>\newrobustcmd</code>, <code>\newrobustcmd*</code>, as well as the commands
<code>\renewrobustcmd</code>, <code>\renewrobustcmd*</code>, and the commands
<code>\providerobustcmd</code>, and <code>\providerobustcmd*</code>.  These are
similar to <code>\newcommand</code>, <code>\newcommand*</code>,
<code>\renewcommand</code>, <code>\renewcommand*</code>, <code>\providecommand</code>, and
<code>\providecommand*</code>, but define a robust <var>cmd</var> with two
advantages as compared to <code>\DeclareRobustCommand</code>:
</p><ol>
<li> They use the low-level e-TeX protection mechanism rather than the
higher level LaTeX <code>\protect</code> mechanism, so they do not incur
the slight loss of performance mentioned above, and
</li><li> They make the same distinction between <code>\new&hellip;</code>,
<code>\renew&hellip;</code>, and <code>\provide&hellip;</code>, as the standard
commands, so they do not just make a log message when you redefine
<var>cmd</var> that already exists, in that case you need to use either
<code>\renew&hellip;</code> or <code>\provide&hellip;</code> or you get an error.
</li></ol>


</dd>
<dt><code>\IfFileExists{<var>file name</var>}{<var>true code</var>}{<var>false code</var>}</code></dt>
<dt><code>\InputIfFileExists{<var>file name</var>}{<var>true code</var>}{<var>false code</var>}</code></dt>
<dd><a name="index-_005cIfFileExists" class="anchor"></a>
<a name="index-_005cInputIfFileExists" class="anchor"></a>
<p>Execute <var>true code</var> if LaTeX finds the file <samp><var>file
name</var></samp> or <var>false code</var> otherwise.  In the first case it executing
<var>true code</var> and then inputs the file.  Thus the command
</p>
<div class="example">
<pre class="example">\IfFileExists{img.pdf}{%
  \includegraphics{img.pdf}}{\typeout{!! img.pdf not found}
</pre></div>

<p>will include the graphic <samp>img.pdf</samp> if it is found and otherwise
give a warning.
</p>
<p>This command looks for the file in all search paths that LaTeX uses,
not only in the current directory.  To look only in the current
directory do something like <code>\IfFileExists{./filename}{<var>true
code</var>}{<var>false code</var>}</code>.  If you ask for a filename without a
<code>.tex</code> extension then LaTeX will first look for the file by
appending the <code>.tex</code>; for more on how LaTeX handles file
extensions see <a href="latex2e_24.html#g_t_005cinput">\input</a>.
</p>
</dd>
<dt><code>\LoadClass[<var>options list</var>]{<var>class name</var>}[<var>release date</var>]</code></dt>
<dt><code>\LoadClassWithOptions{<var>class name</var>}[<var>release date</var>]</code></dt>
<dd><a name="index-_005cLoadClass" class="anchor"></a>
<a name="index-_005cLoadClassWithOptions" class="anchor"></a>
<p>Load a class, as with <code>\documentclass[<var>options
list</var>]{<var>class name</var>}[<var>release info</var>]</code>.  An example is
<code>\LoadClass[twoside]{article}</code>.
</p>
<p>The <var>options list</var>, if present, is a comma-separated list.  The
<var>release date</var> is optional.  If present it must have the form
<var>YYYY/MM/DD</var>.
</p>
<p>If you request a <var>release date</var> and the date of the package
installed on your system is earlier, then you get a warning on the
screen and in the log like this.
</p>
<div class="example">
<pre class="example">You have requested, on input line 4, version `2038/01/19' of
document class article, but only version `2014/09/29 v1.4h
Standard LaTeX document class' is available.
</pre></div>

<p>The command version <code>\LoadClassWithOptions</code> uses the list of
options for the current class.  This means it ignores any options passed
to it via <code>\PassOptionsToClass</code>.  This is a convenience command
that lets you build classes on existing ones, such as the standard
<code>article</code> class, without having to track which options were passed.
</p>
</dd>
<dt><code>\ExecuteOptions{<var>options-list</var>}</code></dt>
<dd><a name="index-_005cExecuteOptions" class="anchor"></a>
<p>For each option <var>option</var> in the <var>options-list</var>, in order, this command
executes the command <code>\ds@<var>option</var></code>.  If this command is not
defined then that option is silently ignored.
</p>
<p>It can be used to provide a default option list before
<code>\ProcessOptions</code>.  For example, if in a class file you want the
default to be 11pt fonts then you could specify
<code>\ExecuteOptions{11pt}\ProcessOptions\relax</code>.
</p>
</dd>
<dt><code>\NeedsTeXFormat{<var>format</var>}[<var>format date</var>]</code></dt>
<dd><a name="index-_005cNeedsTeXFormat" class="anchor"></a>
<p>Specifies the format that this class must be run under.  Often issued
as the first line of a class file, and most often used as:
<code>\NeedsTeXFormat{LaTeX2e}</code>.  When a document using that class is
processed, the format name given here must match the format that is
actually being run (including that the <var>format</var> string is case
sensitive).  If it does not match then execution stops with an error
like &lsquo;<samp>This file needs format `LaTeX2e' but this is `xxx'.</samp>&rsquo;
</p>
<p>To specify a version of the format that you know to have certain
features, include the optional <var>format date</var> on which those features
were implemented.  If present it must be in the form <code>YYYY/MM/DD</code>.
If the format version installed on your system is earlier than
<var>format date</var> then you get a warning like this.
</p>
<div class="example">
<pre class="example">You have requested release `2038/01/20' of LaTeX, but only
release `2016/02/01' is available.
</pre></div>

</dd>
<dt><code>\OptionNotUsed</code></dt>
<dd><a name="index-_005cOptionNotUsed" class="anchor"></a>
<p>Adds the current option to the list of unused options.  Can only be used
within the <var>code</var> argument of either <code>\DeclareOption</code> or
<code>\DeclareOption*</code>.
</p>

</dd>
<dt><code>\PassOptionsToClass{<var>option list</var>}{<var>class name</var>}</code></dt>
<dt><code>\PassOptionsToPackage{<var>option list</var>}{<var>package name</var>}</code></dt>
<dd><a name="index-_005cPassOptionsToClass" class="anchor"></a>
<a name="index-_005cPassOptionsToPackage" class="anchor"></a>
<p>Adds the options in the comma-separated list <var>option list</var> to the
options used by any future <code>\RequirePackage</code> or <code>\usepackage</code>
command for package <var>package name</var> or the class <var>class name</var>.
</p>
<p>The reason for these commands is: you may load a package any number of
times with no options but if you want options then you may only supply
them when you first load the package.  Loading a package with options
more than once will get you an error like <code>Option clash for package
foo.</code> (LaTeX throws an error even if there is no conflict between the
options.)
</p>
<p>If your own code is bringing in a package twice then you can collapse
that to once, for example replacing the two
<code>\RequirePackage[landscape]{geometry}</code> and
<code>\RequirePackage[margins=1in]{geometry}</code> with the single command
<code>\RequirePackage[landscape,margins=1in]{geometry}</code>.
</p>
<p>However, imagine that you are loading <samp>firstpkg</samp> and inside that
package it loads <samp>secondpkg</samp>, and you need the second package to be
loaded with option <code>draft</code>.  Then before doing the first package
you must queue up the options for the second package, like this.
</p>
<div class="example">
<pre class="example">\PassOptionsToPackage{draft}{secondpkg}
\RequirePackage{firstpkg}
</pre></div>

<p>(If <code>firstpkg.sty</code> loads an option in conflict with what you want
then you may have to alter its source.)
</p>
<p>These commands are useful for general users as well as class and package
writers.  For instance, suppose a user wants to load the <code>graphicx</code>
package with the option <code>draft</code> and also wants to use a class
<code>foo</code> that loads the <code>graphicx</code> package, but without that
option. The user could start their LaTeX file with
<code>\PassOptionsToPackage{draft}{graphicx}\documentclass{foo}</code>.
</p>
</dd>
<dt><code>\ProcessOptions</code></dt>
<dt><code>\ProcessOptions*<var>\@options</var></code></dt>
<dd><a name="index-_005cProcessOptions" class="anchor"></a>
<a name="index-_005cProcessOptions_002a" class="anchor"></a>
<p>Execute the code for each option that the user has invoked.  Include it
in the class file as <code>\ProcessOptions\relax</code> (because of the
existence of the starred command).
</p>
<p>Options come in two types.  <em>Local options</em> have been specified for this
particular package in the <var>options</var> argument of
<code>\PassOptionsToPackage{<var>options</var>}</code>,
<code>\usepackage[<var>options</var>]</code>, or
<code>\RequirePackage[<var>options</var>]</code>.  <em>Global options</em> are those given
by the class user in <code>\documentclass[<var>options</var>]</code> (If an option
is specified both locally and globally then it is local.)
</p>
<p>When <code>\ProcessOptions</code> is called for a package <samp>pkg.sty</samp>, the
following happens:
</p><ol>
<li> For each option <var>option</var> so far declared
with <code>\DeclareOption</code>, it looks to see if that option is either a
global or a local option for <code>pkg</code>. If so then it executes the
declared code.  This is done in the order in which these options were
given in <samp>pkg.sty</samp>.
</li><li> For each remaining local option, it executes the command
<code>\ds@</code><var>option</var> if it has been defined somewhere (other than by
a <code>\DeclareOption</code>); otherwise, it executes the default option code
given in <code>\DeclareOption*</code>. If no default option code has been
declared then it gives an error message.  This is done in the order in
which these options were specified.
</li></ol>

<p>When <code>\ProcessOptions</code> is called for a class it works in the same
way except that all options are local, and the default <var>code</var> for
<code>\DeclareOption*</code> is <code>\OptionNotUsed</code> rather than an error.
</p>
<p>The starred version <code>\ProcessOptions*</code> executes the
options in the order specified in the calling commands, rather than in
the order of declaration in the class or package. For a package this
means that the global options are processed first.
</p>
</dd>
<dt><code>\ProvidesClass{<var>class name</var>}[<var>release date</var> <var>brief additional information</var>]</code></dt>
<dt><code>\ProvidesClass{<var>class name</var>}[<var>release date</var>]</code></dt>
<dt><code>\ProvidesPackage{<var>package name</var>}[<var>release date</var> <var>brief additional information</var>]</code></dt>
<dt><code>\ProvidesPackage{<var>package name</var>}[<var>release date</var>]</code></dt>
<dd><a name="index-_005cProvidesClass" class="anchor"></a>
<a name="index-_005cProvidesPackage" class="anchor"></a>
<p>Identifies the class or package, printing a message to the screen and
the log file.
</p>
<p>When you load a class or package, for example with
<code>\documentclass{smcmemo}</code> or <code>\usepackage{test}</code>, LaTeX
inputs a file.  If the name of the file does not match the class or
package name declared in it then you get a warning.  Thus, if you invoke
<code>\documentclass{smcmemo}</code>, and the file <samp>smcmemo.cls</samp> has
the statement <code>\ProvidesClass{xxx}</code> then you get a warning like
<code>You have requested document class `smcmemo', but the document
class provides 'xxx'.</code>  This warning does not prevent LaTeX from
processing the rest of the class file normally.
</p>
<p>If you include the optional argument then you must include a date,
before any spaces, of the form <code>YYYY/MM/DD</code>. The rest of the
optional argument is free-form, although it traditionally identifies the
class, and is written to the screen during compilation and to the log
file.  Thus, if your file <samp>smcmemo.cls</samp> contains the line
<code>\ProvidesClass{smcmemo}[2008/06/01 v1.0 SMC memo class]</code> and
your document&rsquo;s first line is <code>\documentclass{smcmemo}</code> then you
will see <code>Document Class: smcmemo 2008/06/01 v1.0 SMC memo class</code>.
</p>
<p>The date in the optional argument allows class and package users to ask
to be warned if the version of the class or package is earlier than
<var>release date</var>.  For instance, a user could enter
<code>\documentclass{smcmemo}[2018/10/12]</code> or
<code>\usepackage{foo}[[2017/07/07]]</code> to require a class or package
with certain features by specifying that it must be released no earlier
than the given date.  (Although, in practice package users only rarely
include a date, and class users almost never do.)
</p>
</dd>
<dt><code>\ProvidesFile{<var>file name</var>}[<var>additional information</var>]</code></dt>
<dd><a name="index-_005cProvidesFile" class="anchor"></a>
<p>Declare a file other than the main class and package files, such as
configuration files or font definition files.  Put this command in that
file and you get in the log a string like <code>File: test.config
2017/10/12 config file for test.cls</code> for <var>file name</var> equal to
&lsquo;<samp>test.config</samp>&rsquo; and <var>additional information</var> equal to
&lsquo;<samp>2017/10/12 config file for test.cls</samp>&rsquo;.
</p>
</dd>
<dt><code>\RequirePackage[<var>option list</var>]{<var>package name</var>}[<var>release date</var>]</code></dt>
<dt><code>\RequirePackageWithOptions{<var>package name</var>}[<var>release date</var>]</code></dt>
<dd><a name="index-_005cRequirePackage" class="anchor"></a>
<a name="index-_005cRequirePackageWithOptions" class="anchor"></a>
<p>Load a package, like the command <code>\usepackage</code> (see <a href="#Additional-packages">Additional packages</a>). The LaTeX development team strongly recommends use of
these commands over Plain&nbsp;TeX&rsquo;s <code>\input</code>; see the Class
Guide.  An example is
<code>\RequirePackage[landscape,margin=1in]{geometry}</code>.
</p>
<p>The <var>option list</var>, if present, is a comma-separated list.  The
<var>release date</var>, if present, must have the form <var>YYYY/MM/DD</var>.  If
the release date of the package as installed on your system is earlier
than <var>release date</var> then you get a warning like <code>You have
requested, on input line 9, version `2017/07/03' of package jhtest, but
only version `2000/01/01' is available</code>.
</p>
<p>The <code>\RequirePackageWithOptions</code> version uses the list of options
for the current class.  This means it ignores any options passed to it
via <code>\PassOptionsToClass</code>.  This is a convenience command to allow
easily building classes on existing ones without having to track which
options were passed.
</p>
<p>The difference between <code>\usepackage</code> and <code>\RequirePackage</code> is
small.  The <code>\usepackage</code> command is intended for the document file
while <code>\RequirePackage</code> is intended for package and class files.
Thus, using <code>\usepackage</code> before the <code>\documentclass</code> command
causes LaTeX to give error like <code>\usepackage before
\documentclass</code>, but you can use <code>\RequirePackage</code> there.
</p></dd>
</dl>





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